The present invention concerns a radial piston pump with a pump housing, in which a plurality of cylinder bores are made in which pump pistons are inserted, which pistons can be driven by a cam.
Radial piston pumps of many types are widely known. Thus, DE 41 39 611 describes a radial piston pump, the pump pistons of which pull in oil through a suction opening on the upper rim joined to an annular channel. The pressure pulsations in the suction channel, caused by the pump pistons, engender an uneven filling of the piston spaces. Further, a reversal in the flow direction, which again causes an unequal filling of the pistons arises in the said annular channel, dependent on respective pump pistons.
Beyond these disadvantages, the conventional radial piston pumps give rise to noise, because of inherent operating principles, which has proven disturbing when radial piston pumps are used as an oil-pump in a transmission for motor vehicles.
In order to lessen this buildup of noise, the applicant already has proposed a radial piston pump in DE 44 25 929 with a plurality of pump pistons arranged in star shape around a cam, whereby storage spaces are apportioned for the pistons, which said storage spaces are in communication with an annular channel. Thereby, each piston receives non-turbulent oil in the suction line from the said storage space. This contributes to an equal filling of the piston space being achieved at a low level of noise. The interconnection of the said storage spaces between one another allows the installation of only one suction intake, because the same suction relationship has been created at the predetermined oil supply inlet for each piston. A radial piston pump of this kind is especially well adapted for an automatic transmission of a passenger car, wherein the said pump would be placed immediately after the hydrodynamic converter. A cam is installed, as a drive element for the radial piston pump, to turn on the hollow shaft of the converter, whereby the pistons in the radial piston pump are held by the force of compressive springs with their piston bases contacting a slip ring. The pistons slide in the cylinder bores in the pump body, wherein the said cylinder bores are closed by plugs. Each plug has as an exit vent from the pressure chamber, this being a bore, on which a band spring encircling the pump places a closure pressure. The band spring seals the bores from the collection space, which communicates with one or more using apparatuses.
The purpose of the present invention is to design a radial piston pump, for the transmission of a motor vehicle, so that no objectionable sound or pressure pulsations occur.
Basing considerations on a radial piston pump of the kind more precisely defined in the introductory passages, this purpose is achieved by the features provided in claim 1. Advantageous embodiments are described in the subordinate claims.
The invention further provides that an arrangement has been made in the pump pistons which controls both the inlet as well as the outlet of the fluid, that is in or out of each cylinder bore.
By means of the placement of an inlet and an outlet control within the pumping cylinders, the pressure peaks, which up to now have been occurring and which make themselves felt in the collection space, are now prevented or very greatly reduced. In the case of the previously known radial piston pumps with a valve band, a pressure peak must inherently be generated in the cylinder bore, in order to open the valve band against the existing outer pressure. Contrary to this, with the present invention, an effect of accelerating and decelerating on the part of the components within the pump pistons in the form of a check valve is applied so that an inlet and outlet control is formed, which is now largely independent of the pressure relationships inside and outside of the cylinder bore.
A further advantage, which is achieved with the radial piston pump designed in accord with the invention, is that the build up of pressure in the cylinder bore generates itself more quickly since inflow, at the suction intake, is uniform over the entire suction stroke and that, in the case of the subsequent pressure stroke, the inlet is immediately closed, that is to say is more quickly closed than is the case for the previously known radial piston pumps with a slot control.